Purification of isocyanates by reduction of the hydrolyzable chlorine and acid content



United States Patent PURIFICATIGN 9F ISOCYANATES BY REDUC- TION OF THEHYDROLYZABLE CHLORINE AND ACID CONTENT Eugene L. Powers, NewMartinsville, W. Va, assignor to Mobay Chemical Company, Pittsburgh,Pa., 21 corporation of Delaware No Drawing. Continuation-impart ofapplication Ser. No. 395,952, Sept. 11, 1964. This application June 30,1965, Ser. No. 468,619

Claims. (Cl. 269-453) This invention relates to organic isocyanates andto a method of preparing the same and more particularly, to an improvedmethod for removing the hydrolyzable chlorine and reducing the acidityof organic isocyanates prepared by the usual methods. This applicationis a continuation-impart of copending application Ser. No. 395,- 952,filed Sept. 11, 1964, now US. Patent No. 3,264,336.

It is to be understood that the term hydrolyzable chlorine refers tolabile chlorine atoms which are loosely bound in a compound and not to achlorine atom that is tightly chemically bound such as chlorine inchlorobenzene. This value is determined by extracting the chlorine fromthe isocyanate by hot solution in an aqueous-methanol solvent, orliberating the chlorine on hydrolysis of the compound with water. Theextract is then subjected to a potentiometric titration of the chlorideion concentration with a standard silver nitrate solution. From theamount of silver nitrate necessary, the percentage of the hydrolyzablechlorine can be determined by a simple calculation. The term acidity asunderstood here is determined essentially in the same manner as thehydrolyzable chlorine content except dilute caustic is used in thetitration of the free HCl or acid. From the amount of caustic used, thepercent acidity as HCl can be determined.

Organic polyisocyanates are reacted with organic compounds having groupscontaining reactive hydrogen atoms in the preparation of a polyurethaneplastic. The reaction rate of an isocyanate group with a reactivehydrogen atom is reduced by the presence of hydrolyzable chlorine in theisocyanate, which must either be reduced or removed completely in orderto efiectuate the reaction. Slocombe, in US. Patent 2,620,349, proposesto adjust the hydrolyzable chlorine content in order to predetermine thereaction rate of isocyanates. Generally, however, any method ofadjusting the hydrolyzable chlorine and acidity content of an isocyanateinvolves reducing it to a very low value initially by a fractionaldistillation process. A serious problem with a fractional distillationprocess is that if the isocyanate being distilled has a boiling pointnear the boiling point of the hydrolyzable chlorine containing material,then a fractional distillation process is inconvenient, costly, and inmost cases, inoperative. Further, a high boiling isocyanate is difiicultto fractionally distill without high yield losses due to prolongedoverheating.

It is therefore an object of this invention to provide an improvedmethod for reducing the hydrolyzable chlorine and acidity content of anorganic isocyanate.

Another object of this invention is to reduce the hydrolyzable chlorineand acidity content of an organic isocyanate by a'method which avoidscostly and inconvenient distillation steps, thereby allowing one topredetermine the reactivity of the isocyanate with a reactive hydrogenatom.

Still another object of the invention is to adjust the hydrolyzablechlorine and acidity content of an organic isocyanate by a method whichis adapted for use either during the production of the isocyanate orafter the isocyanate has been made.

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in my previous application, Ser. No. 395,952, I disclosed that thehydrolyzable chlorine and acidity content of an organic isocyanate couldbe reduced by treating the isocyanate with an effective amount ofcadmium laurate, cobaltic benzoate and ferric naph'thenate. I have nowfound, however, that the foregoing objects and others which will becomeapparent from the following description may be best accomplished inaccordance with the present invention by treating the isocyanatecontaining hydrolyzable chlorides with an effective amount (that is, andamount sufiicient to reduce the hydrolyzable chlorides) of cadmiumnaphthenate, cobalt naphthenate, copper naphthenate, lead naphthenate,manganese naphthenate or zinc naphthenate or mixtures thereof(hereinafter referred to as metallic compounds) and distilling theresulting mixture to remove the isocyanate. The invention thuscontemplates a method for adjusting the hydrolyzable chlorine andacidity of an organic isocyanate to any predetermined level by firstreducing it through polymerization or decomposition of the hydrolyzablechlorine and acidity compounds in the presence of one of the abovementioned metallic compounds to form a material which can be separatedfrom the isocyanate by distillation, followed by the addition of a knownhydrolyzable chlorine-bearing or compatible acidic material ofpredetermined acidity. The organic isocyanate and metallic compound maybe mixed together in any suitable manner. For example, solid or liquidmetallic compounds can be added to the organic isocyanate. The organicisocyanate can be added to the metallic compound. The metallic compoundcan be dissolved in a solvent therefore which is compatible with theorganic isocyanate and the solution can be mixed with the organicisocyanate. The metallic compound can be added to a solution of thecrude or refined isocyanate or a compatible solvent to form a slurry orsolution and then introduced into a larger amount of isocyanate.

Other compounds such as ferric chloride and iron benzoate have beenproposed heretofore as suitable materials for reducing the hydrolyzablechloride content of isocyanates, but these compounds suffer from adistinct disadvantage in that they are not liquid and therefore cannotbe easily introduced into the production system, requiring specialhandling before they can be used.

It is to be understood that the synthesis of the organic isocyanate doesnot form a part of this invention. The product from any method ofpreparing organic isocyanates which results in the final product havinga hydrolyzable chlorine or acidity content may be treated by the processof this invention to remove the hydrolyzable chlorine containingsubstituents. As an example of a suitable method of preparing organicisocyanates, the corresponding amine or amine salts are reacted withphosgene in the manner known in the art. The following patents set forthprocedures which may be used in the preparation of the organicisocyanates: 2,480,089; 2,- 680,127; 2,680,128; 2,733,254; 2,837,554;2,839,559 and 2,875,225. The phosgenation procedure is generallyutilized in the preparation of isocyanates because of the economy of themethod and the resulting superior yields obtained.

A particularly suitable method of preparing an organic isocyanate is setforth in Canadian Patent 537,484 wherein a solution of phosgene and asolution of an organic amine are introduced into a high speed mixer byseparate conduits. This mixture is then fed to a reactor in which thehot phosgenation step takes place. The solvent in which the amine andphosgene were dissolved is then removed by distillation which isgenerally carried out under a vacuum.

In accordance with this invention, the hydrolyzable chlorine reducingstep may be conducted at any one of a number of stages in the process.For example, the metallic compound may be introduced into a solution ofan organic isocyanate in a solvent immediately after the hotphosgenationstep of the procedure for preparing an isocyanate. It may also beconducted after the inert solvent has been removed from the isocyanateby a distillation step. Of course, since these further steps, such as adistillation or a number of distillation steps, generally are conductedfor the purpose of purifying the organic isocyanate, the hydrolyzablechlorine content and acidity are also generally reduced to a certainextent. Therefore, the amount of the metallic compound which isnecessary to reduce the hydrolyzable chlorine and acidity to a minimumis dependent upon the hydrolyzable chlorine and acidity contentremaining in the isocyanate at the time the mixture with the metalliccompound is carried out. This invention is particularly suitable for thereason that the hydrolyzable chlorine and acidity content may be reducedat any time after the preparation of the isocyanate is completed. Thatis, the isocyanate may be prepared by one manufacturer and shipped to apurchaser who may then reduce the hydrolyzable chlorine and aciditycontent by simply stirring into the isocyanate one of the metalliccompounds mentioned above and then carrying out a simple straightforward distillation.

In accordance with this invention, it has been found that certainmetallic compounds will produce the desired result of reducing thehydrolyzable chlorine and acidity content of organic isocyanates. Themetallic compounds which have been found operable are cadmiumnaphthenate, cobalt naphthenate, copper naphthenate, lead naphthenate,manganese naphthenate, or zinc naphthenate or mixtures thereof. Thetreatment with the metallic compounds is carried out by stirring it intothe hydrolyzable chlorine containing isocyanate, either alone or insolution in an inert solvent. It is preferred that the treatment withthe metallic compound be carried out under anhydrous conditions sincethe presence of water will result in a loss of the isocyanate due to theformation of urea linkages. This procedure may be carried out at anysuitable temperature; however, elevated temperatures are preferred inorder to shorten the period necessary to reduce the hydrolyzablechlorine and acidity content to a minimum. The period of time for thetreatment is dependent upon the temperature at which the treatment iscarried out. The temperature at which the treatment with the metalliccompound should take place is to a certain extent determined by thespecific properties of the isocyanate being treated. That is, thetreatment should be carried out below the boiilng point of theisocyanate and within a range preferably between 50 C. and about 210 C.A period of time of from about 0.5 to about 6 hours is generallysufiicient for the minimum hydrolyzable chlorine or acidity content tobe reached. However, the hydrolyzable chlorine and acidity content isreduced to some degree even when the isocyanate is distilled immediatelyafter the metallic compound is added. After this treatment, the materialincluding the isocyanate, the metallic compound and the hydrolyzablechlorine and acidic materials, is distilled generally under vacuum toremove the organic isocyanate from the residue of hydrolyzable chlorineand acidic containing substituents.

As stated previously, the quantity of the particular metalliccompoundused for treating the organic isocyanates depends on the amount ofhydrolyzable chlorine and acidic containing substituents present in theparticular isocyanate. However, an amount from about 0.01 to about 2 molpercent of any of the materials set forth above is usually suflicient toreduce the hydrolyzable chlorine and acidic content.

The method of the inst-ant invention is applicable to the production ofaliphatic, cycloaliphatic, alkaryl, heterocyclic, and aryl mono-, diandpolyisocyanates. illustrative examples of these are hexyl isocyanate,octyl isocyanate, dodecyl isocyanate, octadecyl isocyanate, ethylenediisocyanate, propylene diisocyanate, tetramethylene di-- dodecyl phenylisocyanate, p-cetyloxyphenyl isocyanate,

m-phenylene diiisocyanate, p-phenylene diisocyanate, nap'hthylene 1,4diisocyanate, naphthylene 1,5 diisocyanate, 1,2,4-benzene triisocyanate,etc., furfuryl iso-.

cyanate, tetrahydrofurfuryl isocyanate, fur'furyl-idene diisocyanate,etc.; p,p,p"-tri-phenylmethane triisocyanate,dipheny1-4,6,4'-triisocyanate and the like. The particular metalliccompound used must be selected with its boiling point and that of theisocyanate sufiiciently different to permit separation by a simpledistillation.

It is again pointed out for the purpose of clarity that this inventionis not limited to particular percentages, temperatures and periods oftime for which this reaction is to take place for the reason that thesevariables are dependent upon the condition of the isocyanate whentreated in the manner specified herein. It the isocyanate is treatedimmediately after removal from the hot-phosgenation step in thepreparationof the isocyanate, at least one of the variables, that is,the period of time, the quantity of the metallic compound used, or thetemperature will exceed that necessary to lower the hydrolyzablechlorine and acidity content of an isocyanate sample which has beentwice distilled. That is, to lower the hydrolyzable chloride and aciditycontent to a given percentage, more of the metallic compound would berequired in a crude isocyaq nate than in a refined isocyanate.

Organic isocyanates treated in accordance with this invention are usefulin the preparation of cellular poly.- urethane materials as well aselastomeric materials. Ceh lular polyurethanes are useful formanufacturing cushions, pillows, upholstering units of all types and forsound and weather insulation purposes. Elastomeric polyurethanes areuseful for the manufacture of vehicle tires, gears, shaft couplings,diaphragms and many other applif cations.

The invention may be further illustrated by the following examples inwhich parts are given by weight unless otherwise specified.

Example 1 A solution of 2,4-tolylene diamine in o-dichlorobenzene havinga concentration of about 15 parts amine to about 285 parts solvent isintimately admixed with liquid phosgene which is at a temperature ofabout 0 C. The temperature of the tolylene diamine solution prior tomixing is about 75 C. The reaction mixture is then heated to atemperature of about C. for about 3 hours while adding an excess ofphosgene. Residual phosgene is next removed by passing nitrogen into thesolution. The solvent is then removed by distillation. The yield of2,4-toluylene diisocyanate is from about 96 percent to about 98 percentof theoretical and has a hydrolyzable chlorine content of about 0.06percent.

The previous example illustrates one method of preparing toluylenediisocyanate from its corresponding di-. amine. No particular steps weretaken to control or reduce the hydrolyzable chlorine content of thematerial.

Examples 2 through are conducted in accordance with the followingprocedure.

The 2,4-toluylene diisocyanate reaction product of Example 1 isintroduced in a vessel equipped with an agitating device. The metalliccompound is then introduced in the form of a slurry in the 2,4-toluylenediisocyanate and the entire mixture stirred and heated for four hours at150 C. The toluylene diisocyanate is then removed by vacuumdistillation. The conditions of the treatment and results of theseexamples are set forth in the following table.

0.75 g. Catalyst per 500 g. TDI

Example No. Compound R0. in Refined Residue T I, After PercentTreatment,

Percent 2 Cadmium Naphthenate-.- 0. 034 1 3- Cobalt N aphthenate 0. 0291 4- Copper N aphthenate- 0. 031 1 5- Lead Naphthenate 0. 024 1. 6 61Manganese N aphthenate 0. 020 1 7- Zine N aphthenate 0. 025 1 8-.--Control (none) 0.046 1 7. 5 g. Catalyst per 500 g.

TDI Example N 0. Compound H.C. in Refined Residue TDI, After PercentTreatment,

Percent 9 Cadmium Naphthenate 001 1. 7 10- Cobalt N aphthenate 001 4. 0001 1. 7 001 33. 8 005 4. 0 001 2. 2

It will be noted from Examples 9 through 14 that an increased amount ofthe metallic compound will result in a product having substantially nochlorides.

Of course, it is to be understood that any of the previously mentionedisocyanates may be treated in the manner set forth in the examples andthat the invention is not limited to only the particular isocyanates setforth in the examples. Further, any of the materials set forthpreviously as the treating compound may be substituted into the examplesto reduce the hydrolyzable chlorine content.

Although the invention has been described in considerable detail for thepurpose of illustration, it is to be understood that variations may bemade therein by those skilled in the art without departing from thespirit of the invention and the scope of the claims.

What is claimed is:

1. A method of reducing the hydrolyzable chlorine and acidity content oforganic isocyanates containing hydrolyzable chlorides which comprisesmixing with the organic isocyanate an amount of a compound selected fromthe group consisting of cadmium naphthenate, cobalt naphthenate, coppernaphthenate, lead naphthenate, manganese naphthenate, zinc naphthenate,and mixtures thereof sufficient to reduce the hydrolyzable chlorides inthe isocyanate and distilling the mixture to separate the isocyanate.

2. A method of reducing the hydrolyzable chlorine and acidity content oforganic isocyanates containing hydrolyzable chlorides which comprisesmixing with the organic isocyanate from about 0.01 to about 2 molpercent based on said organic isocyanate of a member selected from thegroup consisting of cadmium naphthenate, cobalt naphthenate, coppernaphthenate, lead naphthenate, manganese naphthenate, zinc naphthenate,and mixtures thereof and distilling the mixture to separate theisocyanate.

3. The process of claim 1 wherein the group member is cadmiumnaphthenate.

4. The process of claim 1 wherein the group member is cobaltnaphthenate.

5. The process of claim 1 wherein the group member is coppernaphthenate.

6. The process of claim 1 wherein the group member is lead naphthenate.

7. The process of claim 1 wherein the group member is manganesenaphthenate.

8. The process of claim 1 wherein the group member is zinc naphthenate.

9. A method of reducing the hydrolyzable chlorides and acidity contentof organic isocyanates containing hydrolyzable chlorides which comprisesmixing with the organic isocyanate from about 0.01 to about 2 molpercent based on the organic isocyanate of a member selected from thegroup consisting of cadmium naphthenate, cobalt naphthenate, coppernaphthenate, lead naphthenate, manganese naphthenate, zinc naphthenateand mixtures thereof and heating the mixture at a temperature below theboiling point of the isocyanate for from about 0.5 to about 6 hours, anddistilling the mixture to separate the isocyanate.

10. A method of reducing the hydrolyzable chlorides and acidity contentof organic isocyanates containing hydrolyzable chlorides which comprisesmixing with the organic isocyanate from about 0.01 to about 2 molpercent based on the organic isocyanate of a member selected from thegroup consisting of cadmium naphthenate, cobalt naphthenate, coppernaphthenate, lead naphthenate, manganese naphthenate, zinc naphthenateand mixtures thereof and heating the mixture at a temperature of fromabout 50 C. to about 210 C. for from about 0.5 to about 6 hours, anddistilling the mixture to separate the isocyanate.

References Cited UNITED STATES PATENTS 3,155,699 11/1964 Powers 260-453CHARLES B. PARKER, Primary Examiner. D. H. TORRENCE, Assistant Examiner.

1. A METHOD OF REDUCING THE HYDROLZABLE CHLORINE AND ACIDITY CONTENT OFORGANIC ISOCYANATES CONTAINING HYDROLYZABLE CHLORIDES WHICH COMPRISESMIXING WITH THE ORGANIC ISOCYANATE AN AMOUNT OF A COMPOUND SELECTED FROMTHE GROUP CONSISTING OF CADMIUM NAPHTHENATE, COBALT NAPHTHENATE, COPPERNAPHTHENATE, LEAD NAPHTHENATE, MANGANESE NAPHTHENATE, ZINC NAPHTHENATE,AND MIXTURES THEREOF SUFFICIENT TO REDUCE THE HYDROLYZABLE CHLORIDES INTHE ISOCYANATE AND DISTILLING THE MIXTURE TO SEPARATE THE ISOCYANATE.